Showing papers by "V. Fernao Pires published in 2022"

Design and Multiobjective Optimization of A Double-stator Axial Flux SRM with Full-pitch Winding Configuration

Abstract: In this paper, a novel axial flux double stator switched reluctance motor (AFDSSRM) is presented and optimized for electric vehicles application. AFDSSRM adopts the axial arrangement of double stator and inner rotor structure with full-pitch winding configuration. The flux generated by the two stators cancel each other at the unaligned position, then a low unaligned inductance barely affected by saturation is achieved, which is the primary advantage of the AFDSSRM. First, the topology and power equation of the motor are presented briefly. Due to a large number of dimensional parameters of the proposed structure, comprehensive sensitivity analysis is used to classify the design parameters into strong-sensitive and weak-sensitive classes, and a multi-layer optimization approach is adopted for the variables of both classes. The response surface method combined with the multiobjective genetic algorithm is employed to optimize the strong-sensitive variables, while the Taguchi algorithm is applied to optimize the weak-sensitive variables. Moreover, the 3D finite element model is established to analyze the electromagnetic characteristics of the motor. Finally, a prototype motor is manufactured, and the experimental results verify the effectiveness of the proposed structure and optimization method.

PV Generator-Fed Water Pumping System Based on a SRM with a Multilevel Fault-Tolerant Converter

Abstract: This paper presents a pumping system supplied by a PV generator that is based on a switched reluctance machine (SRM). Water pumping systems are fundamental in many applications. Most of them can be used only during the day; therefore, they are highly recommended for use with PV generators. For the interface between the PV panels and the motor, a new multilevel converter is proposed. This converter is designed in order to ensure fault-tolerant capability for open switch faults. The converter is based on two three-level inverters, with some extra switches. Moreover, to reduce the number of switches, the converter is designed to provide inverse currents in the motor windings. Due to the characteristics of this motor, the inverse currents do not change the torque direction. In this way, it was possible to obtain an SRM drive with fault-tolerant capability for transistor faults; it is also a low-cost solution, due to the reduced number of switches and drives. These characteristics of fault-tolerant capability and low cost are important in applications such as water pumping systems supplied by PV generators. The proposed system was verified by several tests that were carried out by a simulation program. The experimental results, obtained from a laboratory prototype, are also presented, with the purpose of validating the simulation tests.

Fault-Tolerant Multilevel Converter to Feed a Switched Reluctance Machine

Abstract: The switched reluctance machine (SRM) is one of the most interesting machines, being adopted for many applications. However, this machine requires a power electronic converter that usually is the most fragile element of the system. Thus, in order to ensure high reliability for this system, it is fundamental to design a power electronic converter with fault-tolerant capability. In this context, a new solution is proposed to give this capability to the system. This converter was designed with the purpose to ensure fault-tolerant capability to two types of switch faults, namely open- and short-circuit. Moreover, apart from this feature, the proposed topology is characterized by a multilevel operation that allows improvement of the performance of the SRM, taking into consideration a wide speed range. Although the proposed solution is presented for an 8/6 SRM, it can be used for other configurations. The operation of the proposed topology will be described for the two modes, fault-tolerant and normal operation. Another aspect that is addressed in this paper is the proposal of fault detection and diagnosis method for this fault-tolerant inverter. It was specifically developed for a multilevel SRM drive. The theoretical assumptions will be verified through two different types of tests, firstly by simulation and secondly by experiments with a laboratory prototype.

Compensation of Unbalanced Low-Voltage Grids Using a Photovoltaic Generation System with a Dual Four-Leg, Two-Level Inverter

Abstract: In this paper, a grid-connected photovoltaic (PV) generation system is proposed with the purpose of providing support to low-voltage grids, namely through the elimination or attenuation of the grid imbalances. This compensation must consider the load types, which can be either linear or non-linear, and whether the reactive power and current harmonics generated by the non-linear loads need to be compensated in addition to the unbalanced active power. This must be well considered, since the compensation of all aspects requires oversized PV inverters. Thus, the different unbalanced compensation schemes are addressed. Several schemes for the generation of the inverter current references taking into consideration the compensation and load type are presented. For this PV generation system, a dual four-leg, two-level inverter is proposed. It provides full unbalanced compensation owing to the fourth leg of the inverter and also extends the AC voltage, which is important when this compensation is required. To control this inverter, a control scheme for the inverter that considers several compensation factors is proposed. A vector voltage modulator associated with the controller is another aspect that is addressed in the paper. This modulator considers the balance between the DC voltages of the inverters. Several compensation schemes are verified through computational tests. The results validate the effectiveness of the proposed PV generation system.

Smart Grid as a Key Tool for the Future of Electrical Distribution Networks

Abstract: A new paradigm has appeared in the electricity sector with the rapid development of new renewable energy sources, storage systems, information and communication technologies, and ways of integrating distributed energy sources [...]

Multi-conductor Line Models for Harmonic Load-flow Calculations in LV Networks with High Penetration of PV Generation

Abstract: Low-voltage (LV) distribution networks are unbalanced and present loads with nonlinear behavior, which introduce harmonics in the networks. The predictable increase in photovoltaic microgeneration (PV µG) accentuates this unbalanced characteristic, as well as poses new technical problems, namely voltage rise and reverse power flow. To accurately account for the distributed PV and loads in the LV network, unbalanced three-phase power flow algorithms should be utilized, where different approaches may be used to represent lines with various degrees of accuracy. The more accurate algorithm considers the electromagnetic coupling between the line conductors, whereas the simpler algorithm represents each conductor of the line as a single-phase line with pure resistive behavior. This paper aims to analyze the influence of the line model on the load flow in a highly unbalanced LV network with a high penetration of PV production, and considers the impact of the harmonics produced by nonlinear loads. Based on the results obtained, it is possible to identify the most suitable model to be used, depending on the study to be performed. Different scenarios of PV generation and loads are addressed in this paper.

Fault-Tolerant Three-Phase VSI Based on a Modified Impedance Source Boost Inverter

Abstract: This article proposes a fault-tolerant solution for the three-phase dc–ac converter using a modified impedance source boost inverter. Besides the additional modified impedance source, the solution is based on the reconfiguration of the topology to maintain the desired operation in case of an open-circuit failure mode of a power device. The proposed topology presents important features such as a boost capability to operate under fault condition and avoid extra active power devices in normal operation (without failures). Besides that, the circuit does not require dead times between the switches of each leg, which increases the reliability of the topology. Regarding the control solution for this converter, it is adopted a closed-loop current controller combined with a vectorial voltage modulator. Since this modulator is also function of the shoot-through, it will be possible to recover the amplitude voltage space vectors due to failures in power devices. The combination of these elements allows to obtain three-phase balanced ac currents with reduced total harmonic distortion even in fault-tolerant operation mode. The fault-tolerant performance of this solution is confirmed through several simulations and experimental results.

A DC-DC Converter with Capability to Support the Voltage Balance of DC Bipolar Microgrids

Abstract: Bipolar DC microgrids are now starting to become an interesting solution for power distribution. Although presenting several advantages over DC unipolar microgrids, bipolar DC has the intrinsic problem of voltage unbalance that may appear depending on the converter topology and load sharing. Therefore, this paper presents a new DC-DC converter topology that can be used with renewable energy sources and has the capability to simultaneously ensure the bipolar microgrid voltage balance. The operation of the proposed topology together with its characteristics is described. A theoretical study of this converter will also be presented, complemented by a set of results from computer simulations. To support these simulations, results from a laboratory prototype will also be displayed. The voltage balance capability of the converter will be checked experimentally.

Interlink Converter for Hybrid AC to Bipolar DC Microgrid or to Two DC Microgrids

Abstract: Due to the new paradigm in which AC grids must coexist with DC microgrids, new solutions to interlink those networks are required. In this context, a new interlink hybrid converter is presented in this paper. This solution is designed to interlink AC grids and bipolar DC microgrids or two DC microgrids. The simplest solution allows linking a three-phase AC grid using only two single-phase inverters. However, it can be extended with the purpose to make a multilevel converter. The solution allows to transfer the energy in a way that supports the attenuation of the voltage unbalance that can appear in the DC microgrid(s). This support is done by an independent transference of energy to the microgrid poles or microgrids. This concept and behavior of the interlink hybrid converter will be tested through simulation studies. The results obtained in these studies show the capability of the proposed solution.

Three-Level T-Type qZ Source Inverter as Grid-Following Unit for Distributed Energy Resources

Abstract: Distributed energy resources (DERs), such as solar photovoltaics (PVs), are required to achieve a high performance and an efficient use of generated renewable power in grid-integrated applications, both in normal and fault operating conditions. In this article, a grid-following (GFL) multifunctional control strategy for a three-phase three-level T-type quasi-impedance source inverter (3L-T-type qZSI) is studied through simulation and experimental tests. The GFL functionality is achieved by a proportional–integral (PI)-based dq current controller for the active and the reactive power tracking. A PI-based dc controller is used for the dc-link voltage control by taking advantage of the quasi-impedance source (qZS) network ability for input voltage boosting. The dc–ac power conversion is accomplished through a space vector pulsewidth modulation (SVPWM) with inner capacitors voltages balancing capability and minimum common-mode voltage (CMV) generation. Besides, a low-voltage ride-through (LVRT) strategy was implemented to fulfill the fault requirements imposed by the Spanish standard. The simulation and experimental results demonstrate the abovementioned functionalities and validate the stability and good dynamic response of the grid-connected 3L-T-type qZSI. Thus, this work supposes a novel contribution due to the few works previously reported in the literature concerning the performance of this relatively recent inverter topology in grid-tied applications.

Synthetic Sensorless Control Scheme for Full-Speed Range of Switched Reluctance Machine Drives With Fault-Tolerant Capability

Abstract: In this article, a synthetic sensorless control scheme for full-speed range of switched reluctance machine (SRM) drives with phase absence fault-tolerant capability is proposed, which integrates the phase inductance gradient detection and the idle phase inductance threshold comparison. First, in each excitation period, only the demagnetization inductance slope negative-going zero-crossing detection (D-ISNZ) is performed to avoid the erroneous aligned position estimation in the main excitation region. Then, considering the sensitivity of the D-ISNZ method to demagnetization regions, the remedial sensorless control strategy based on single inductance threshold (SIT) is adopted. Also, the synthetic algorithm is developed for the seamless combination between the two sensorless methods. To enhance the reliability of sensorless operation, a fault-tolerant rotor position estimation method considering speed transient and phase deviation compensation is also presented. Furthermore, to ensure stable sensorless starting, a commutation instant direct estimation method based on online determined double inductance thresholds is developed. The proposed sensorless control scheme can achieve robustness operation under various working conditions without any prior knowledge of magnetic characteristics, large storage memory occupations, and intensive computations. Experiments are conducted on a three-phase 12/8 SRM experimental setup to verify the feasibility of the proposed sensorless control scheme.

An 8/6 SRM Drive with a Multilevel Converter Based on an NPC Structure and Designed to Provide Transistor Fault Tolerant Capability

Abstract: The use of multilevel topologies in Switched Reluctance Machines (SRM) drives has been verified as a valuable asset. Another essential aspect in these drives, for many applications, is to present the capability to operate under some fault in the power transistors. Thus, in this paper, a new topology of a multilevel converter is presented, to be used in SRM drives presenting transistor fault tolerant capability. This topology was created with the purpose of avoiding using extra transistors excess number and static or mechanical relays. The fault tolerant capability is related not only to open circuit but also to short-circuit fault. The description and operation in normal and fault tolerant mode will be included. The new topology has been tested and verified through a set of simulation tests. The results that can be verified from those tests allow to confirm the characteristics and capability of the proposed SRM drive.

Stability Analysis of Stacked Interleaved DC-DC Step-Down Converter for Resistance Welding Application

Abstract: The study proposes stacked interleaved DC-DC step-down converter with low output ripple level for resistance welding application. The low ripple level in the output allows to provide high quality junctions of small-scale details without splashes of metal. Accurate state-space model of the converter is used to analyze converter stability by means of Nyquist stability criterion. The results show that the proposed stacked interleaved DC-DC step-down converter stays stable regardless of the variations of duty cycle.

A SRM for a PV Powered Water Pumping System Based on a Multilevel Converter and DC/DC Dual Output Converter

Abstract: This paper focuses on a proposal for a system based on a photovoltaic (PV) supply for a powered water pumping. The system consists in a switched reluctance machine (SRM) controlled by a multilevel converter and fed by PV panels associated to a DC/DC converter. The multilevel power converter proposed to control the SRM was designed to minimize the switches and to support the balance of the two input capacitors. The DC/DC converter consists in a hybrid solution that merges a Buck-Boost converter with a Sepic converter. They use a topology solution in which the input current presents a reduced ripple and only requires one switch. This DC/DC converter is also characterized by a dual output to adapt to the multilevel converter. The control system and a maximum power point tracking (MPPT) algorithm are also presented. The operation of this system will be verified by tests that are done by computer simulations.

A Model Predictive Controller for a Buck-Boost Rectifier of an Electric Vehicle Integrated Battery Charger with a Dual-Inverter Drive

Abstract: This paper presents a predictive control system for the front-end Buck-Boost rectifier of an electric vehicle fitted with an integrated battery charger. The drive of this electric vehicle is based on a dual inverter connected to the open-windings induction motor. The rectifier of the integrated charger is based on the high-power factor AC-DC current source converter presenting Buck-Boost characteristics. This converter allows an easy integration in the electric vehicle charger, as well as zero average torque during the charging process. However, existing control systems for this front-end Buck-Boost rectifier are complex and hard to tune. To automate the rectifier vector selection, this paper proposes the use of a model predictive controller (MPC) to control the three-phase charger rectifier AC currents and the voltages capacitors of the dual inverter. Several simulation tests of the AC currents MPC controlled show nearly sinusoidal input currents and near unity power factor operation.

Combining Power Electronic Converters and Automation to Simulate Solar PV systems

Abstract: This paper presents a solar photovoltaic panel simulator system with the ability to perform automatic tests in different condition according to manufacture parameters. This simulator is based on three buck-boost DC-DC converters controlled by a microcontroller and supported by a Programmable Logic Controller which is responsible for the automatic tests. This solution will allow to achieve fast response, like suddenly changes in the irradiation, temperature, or load. To control the power converter, it will be used a fast and robust sliding mode controller. Therefore, with the proposed system is possible to perform the I-V curve simulation of a solar PV panel, evaluate different MPPT algorithms considering different meteorological and load variation. The main advantage of this work is the possibility to evaluate and test several MPPT algorithms and understand the operation and typical operation of solar PV panels in different conditions. Several simulations and experimental results from a laboratory prototype are presented to confirm the theoretical operation.

3L-T-type qZSI as Grid-Forming Unit in ac Microgrid

Abstract: As power systems move towards decentralized models based on renewable energy sources with distributed generation, the role of power inverters in microgrids becomes increasingly important. In this paper, a three-level T-type quasi-impedance source inverter (3L-T-type qZSI) with a grid-forming control structure is studied for the first time in an islanded ac microgrid composed by three prosumers, supplying residential loads. The power sharing among prosumers is achieved through the well-known droop control method with virtual impedance, and proportional-resonant (PR) controller-based voltage and current control loops. A proportional-integral (PI) based control for regulating the dc-link voltage of the T-Type inverter was implemented making use of the boost ability of the qZS network. The proper operation of the microgrid has been tested by simulation with PLECS, demonstrating a robust behavior of the overall system and a good dynamic performance of the proposed control structure for the 3L-T-Type qZSI in different conditions.

A Three-Phase On-Board Integrated Battery Charger for EVs using a Drive Based on Triple Inverters

Abstract: This work presents a three-phase on-board integrated battery charger for electric vehicles with a three-phase machine with open windings. The vehicle motor is supplied by a modular multilevel inverter composed by three three-phase inverters. The input of the charger will operate as a three-phase power factor correction converter and present output Buck-Boost features. In the proposed solution, all windings of the motor are used as DC inductors of the battery charger in a way that will result in a torque cancellation. A detailed description and analysis of the proposed on-board integrated battery charger is presented in this paper. On the other hand, an associated fast and active current controller is also proposed to ensure the unit power factor of the rectifier. The feasibility, characteristics and validation of theoretical deductions will be confirmed through several simulation tests.

Mutilevel Bipolar Back-to-Back HVDC Transmission System Based on the Dual Inverter Converter Structure with Model Predictive Control

Abstract: High-Voltage Direct-Current (HVDC) is an attractive solution to conventional ac transmission systems, to transmit bulk electric power over long distances. Multilevel bipolar back-to-back dual inverters convey advantages to HVDC systems, at the cost of increased difficulties to control the AC currents and DC link voltage. This paper presents a control approach for a bipolar HVDC transmission system based on a dual two-level inverter topology with a multilevel structure. For both multilevel inverter AC sides a model predictive control strategy is designed to control active and reactive power, establishing AC grid currents in the sending and receiving ends. The multilevel converter also guarantees the balancing of the DC bus capacitor voltages. To test the performance and effectiveness of this proposed control strategy, several simulation studies are presented and discussed.

A Fault Diagnosis Scheme Based on the Normalized Indexes of the Images eccentricity for a Multilevel Converter of a Switched Reluctance Motor Drive

Abstract: This paper addresses the fault detection and diagnosis of a fault in the switches of the Switched Reluctance Machine (SRM) power electronic converter. Due to the advantages of using multilevel converters with these machines, a fault detection and diagnosis algorithm is proposed for this converter. The topology under consideration is the asymmetric Neutral Point Clamped (ANPC), and the algorithm was developed to detect open and short circuit faults. The proposed algorithm is based on an approach that discriminates eccentricity of the images formed by the converter voltages. This discrimination is realized through the development of normalized indexes based on the entropy theory. Besides the different fault type the algorithm is also able to detect the transistor under fault. The possibility to implement the proposed approach will be verified through simulation tests.

Bidirectional DC-DC Converter for Battery Storage Systems with Support for Mitigation of Voltage Imbalance in Bipolar DC Microgrids

Abstract: Nowadays DC microgrids provide a valuable alternative to AC technology in the context of electrical energy distribution grids and increasing energy demand. One of the main structures of DC microgrids are the bipolar solutions. Although presenting several advantages over unipolar solutions, the major problem is the voltage imbalance that can appear. This paper presents a non-isolated bipolar DC-DC converter to be integrated in battery storage systems. The converter was designed to transfer energy between the DC microgrid and batteries, and at the same time, to support the balance of the bipolar DC microgrid. This support can be achieved in two ways, namely through the transference of the energy between the DC microgrid and batteries using only the pole that requires support for the balance or as a standalone voltage balancer. Simulations and experimental results of the DC-DC converter operating in bidirectional mode will be provided. From the presented results, it will be possible to verify the capability of the converter to operate as bidirectional interlink between the battery storage systems and the bipolar DC microgrid.

A Fault Tolerant Multilevel Converter Topology for an 8/6 SRM Drive Based on a Cross-Switched Configuration

Abstract: In this paper it is proposed a power electronic converter for an 8/6 SRM drive. The topology is characterized by multilevel characteristics allowing to improve the performance of the machine specially for wide range of speed variation. Besides that it provides fault tolerance to open faults that can occur in the transistors of the converter. With the purpose to reduce the number of transistors the topology was based on the crossover switches configuration. The topology will be described in a detailed way for normal and fault tolerant mode. On the other hand, the proposed power electronic converter will be tested and analyzed through the implementation of the system in a simulation tool. The results that are obtained from this tool confirm the characteristics of the proposed drive. The operation in fault tolerance can be realized in any operation speed.

A Model Predictive Control for a Multilevel Inverter Fed Induction Motor Drive Based on Three-Phase Triple Inverter Modular Topology

Abstract: Induction motor drives based on multilevel inverters have been established as a solution for many applications. Due to their interesting characteristics, several topologies have been proposed. One of the latest topologies is the one based on three-phase triple inverter modular topology. However, not much work has been realized regarding their control. Thus a field-oriented controller with a model predictive control (MPC) strategy to control this AC drive is proposed. The MPC will be used to control the AC currents of the inverter. One aspect that is inherent to this drive is the high number of voltage vectors. Thus, besides their predictive characteristic, this controller also shows their advantage dealing with this high number of voltage vectors. The capabilities of the proposed controller will be verified through a simulation study.